Automations → Automation e-mails. One automation e-mail may serve in several automations, and several times in the same one.
Create an e-mail
New e-mail: a name (“Welcome”) and an editor. The editing page holds:
Save the e-mail (or ⌘ S). The Focus mode button at the top gives the whole screen to the writing.
As with a campaign, put {{ unsubscribe_url }} and {{ organisation.address }} in the content or in the template. Every e-mail also carries the one-click unsubscribe header.
Statistics
At the top of the page, from the first sends: Sent, Opens, Clicks, Bounces, then the most clicked links with how many people clicked them. The list of automation e-mails shows the same figures for each of them.
To tell whether a journey works, read those figures together with the waiting here and passed counters of the action editor.
Delete
Deleting an e-mail breaks no journey: the automations that send it will skip it. 
